Lambert I of Leuven (The Bearded) (born in Leuven, Belgium c950, died in Florennes, Belgium Sept 12, 1015) was the first Count of Leuven. He was killed by Godfrey II, Duke of Lower Lorraine in battle for Godfrey's claim of Count of Verdun.

He was the son of Regnier III, Count of Hainaut and Adela, brother of Reginar IV, Count of Mons, husband of Gerberga of Lower Lorraine, and father of two other counts of Leuven, Henry I of Leuven and Lambert II of Leuven along with Matilda of Leuven (Maud).